Optical Wireless Communication using Digital Pulse Interval Modulation

1
An Ultrafast 1xM All-optical WDM Packet-Switched
Router based on the PPM Header Address
M. F. Chiang1, Z. Ghassemlooy1, W. P. Ng1, H.
Le Minh2, and A. Abd El Aziz1 1. Optical
Communications Research Group School of
Computing, Engineering and Information
Sciences Northumbria University, Newcastle upon
Tyne, UK 2. Department of Engineering Science,
University of Oxford, UK http//soe.unn.ac.uk/ocr
/
2
Contents

• Introduction
• Packets with PPM Address
• PPM Address Correlation
• Proposed Node Architecture
• Simulation Results
• Conclusions

3
Introduction- Research Aim (1)

• There is a growing demand for all optical
  switches and routers at very high speed, to avoid
  the bottleneck imposed by the electronic
  switches.
• In KEOPS1 (keys to optical packet switching) a
  EU project, the packet payload are maintained,
  But the packet header addresses are transmitted
  at low bit-rate and processed in electrical
  domain.

• We present a router architecture employing
  all-optical switches, such as symmetric
  Mach-Zehnder (SMZ).

1C. Guillemot, etc., "Transparent Optical Packet
Switching The European ACTS KEOPS Project
Approach," IEEE Light. Tech., vol. 16, pp.
2117-2134, 1998.
4
Introduction- Research Aim (2)

• In large dimension networks (routing table with
  hundreds or thousands of entries)
• packet processing ?
  throughput latency
• IST-LASAGNE2 project - packet label/addressing
• all-optical employing a cascade of SOA-MZI
  structure
• requiring large number of SOA-MZI swiches are
  increasing as the numbers of the address bit
  increase.

• We present an optical router,
• - where packet header and the routing table
  entries are converted from a
• binary RZ into a pulse position modulation
  (PPM) format.
• - uses only a single AND operation for address
  correlation.
• - offers reduced packet processing time - size
  of the PPM routing table is
• significantly reduced.

• Base on the PPM header address processing, we
  propose an all-optical 1xM WDM router
  architecture for packet routing at multiple
  wavelengths simultaneously, with no wavelength
  conversion modules.

2 F. Ramos, etc., "IST-LASAGNE Towards
All-Optical Label Swapping Employing Optical
Logic Gates and Optical Flip-Flops," IEEE Light.
Tech., vol. 23, pp. 2993-3011, 2005.
5
Introduction- Optical Networks
6
Introduction- Optical Packets

• An optical packet is composed of three parts
• Clock bit For synchronisation purpose
• Address bits Destination of the packet
• Payload bits The really information desired to
  be transmitted

7
Packets with PPM Address

Packet with binary address bits
Packet with PPM address bits



8
PPM Routing Table
Binary RT
PPRT
9
Address Correlation
10
The Architecture of a PPM Header Processing Node
(PPM-HP)
CEM clock extraction module PPM-HEM PPM header
address extraction module PPRT PPM Routing
Table OS All-optical switches, OSC OS control
module
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Operation of PPM-HP
All-optical Switch
Port 1
OSW1
Port 2

OSW2

Port M
OSWM
Header Extraction
CP 1
CP 2
PPRT
CP M
OSWC

1
Entry 1
Clock Extraction
OSWC
Entry 2
2
Synchronisation



Entry M
OSWC
M
PPM-HP
12
1xM All-optical Packet-switched WDM Router


PPM
-
H
P 1

WDM





MUX

Output 1


e

1
E

E

E

E

M
1
2
3
WDM
D E M U X
PPM
-
H
P 2





MUX


Output 2
...




e
Input
2


E

E

E

E



M
1
2
3
WDM




PPM
-
H
P
L
MUX




Output
M


e

M
E

E

E

E

1
2
3
M
L The numbers of input wavelengths M The
numbers of the output ports (In this simulation
L 2 and M 3)
13
Simulation Results- Simulation Parameters
Simulation Tool Virtual Photonic Inc. (VPI)
14
Simulation Results- Time Waveforms
(a) Packets at the inputs of the WDM router and
PPM-HP12
15
Simulation Results- Time Waveforms
(b) Packets observed at the output 1 of the WDM
router and PPM-HP12 (the inset shows the power
fluctuation observed at the output 1 of PPM-HP1)
16
Simulation Results- Time Waveforms
(c) Packets observed at the output 2 of the WDM
router, PPM-HP12
17
Simulation Results- Time Waveforms
(d) packets observed at the output 3 of the WDM
router and PPM-HP12
18
Simulation Results- Channel Crosstalk (CXT)
Two packets at ?1 (packet 1 with address 4) and
?2 (packet 2 with address 4) are sequentially
applied to the input of the WDM router for
measuring the channel CXT.
Pnt is the peak output signal power of all
non-target channels (undesired wavelength). Pt
is the average output signal power of the target
channel (desired wavelength).
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Simulation Results- Channel Crosstalk (CXT)

• 1 THz gt ?f gt 0.8 THz
• CXTinput lt CXToutput
• CXToutput is constant at -27 dB for 1 THz gt ?f gt
  0.4 THz and increasing exponentially. (Minimum
  level of CXToutput is limited by the contrast
  ratio of the extracted clock signals from the
  CEM.)

Input
Output

• 0.8THz gt ?f gt 0.4THz,
• CXToutput lt CXTinput
• Improvement is due to low power
• levels (lt.4 mW) of signals
• emerging from the
• demultiplexer at wavelengths
• other than desired Wavelength.
• Thus not affecting the CEM,
• PPM-HEM and AND Gates.

channel spacing ?f f2 f1
(the bandwidth of the WDM multiplexers and
demultiplexer is 500 GHz)
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Conclusions

• In this paper, a node architecture, operation
  principle and performance of the all-optical WDM
  router based on PPM formatted header address and
  routing table were presented.
• It was shown that the proposed router can
  operate at 160 Gb/s with 0.3 dB of power
  fluctuations observed at the output ports and a
  channel CXT of -27 dB at a channel spacing of
  greater than 0.4 THz and a demultiplexer
  bandwidth of 500 GHz.
• The proposed WDM router routing with no
  wavelength conversion modules offers fast
  processing time and reduced system complexity and
  is capable of operating in the unicast, multicast
  and broadcast transmission modes.

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• Thank You !

Question?